Integrating chemostratigraphy in the modification and improvement of well correlation in the offshore Niger Delta

The Niger Delta is a stratigraphically complex fluvial system of Tertiary age. A total of 15 ditch cutting samples were obtained within the interval of interest, from which 3 wells were subjected to inorganic geochemical and mineralogical analysis to determine the major and trace element concentrations. Inferences from the results show that the Agbada Formation is divided into four Chemostratigraphic mega zones, 12 geochemical units and 9 sand units with geochemical boundaries for DS well at depths of 12,300 ft to 13,500 ft and 7,840 ft to 8,660 ft for ML 1 Well, and ML 2 well at depth 13,240 ft to 14,530 ft. Changes in values of Ga/Rb and Al2O3/(CaO+ MgO+K2O+Na2O) indicate warmer paleoclimate and increasingly intense hydrolytic weathering, marking a sustained change in the paleoclimate. The high percentage concentration of Al2O3 is an indication of abundant clay minerals, whereas the high concentration of Zr suggests sedimentary reworking of the sediments. High V/Ni against Co/Mo ratio concentration intensified upwelling, particularly in those restricted depths was favoured by palaeogeography and significant fluvial input. Conditions could readily evolve from poorly oxygenated to anoxic, the latter state being geochemically the most significant condition. The major oxides trace elements revealed four chemostratigraphic boundaries for DS. ML 1 and ML 2 wells, respectively. The information from V/Sc, Ni/V and V/(V+Ni) ratios indicates the prevalence of anoxic conditions. The redox-sensitive trace elements of the shaly middle parts of the well suggest dysoxic–anoxic conditions, and in most parts of the ML 2 well. Ratios of SiO2 and Al2O3 correspond to sedimentary facies, namely sandstone, siltstone and claystone, while variation in ratios of Cd/Ba and Al2O3/(Na2O+CaO+K2O+MgO) depicts fluctuating paleoclimate during the deposition of the sedimentary sequence. Geochemical values of Cr/Al2O3, Cr/Na2O and Nb/Al2O3 relate to changes in sediment provenance and indicate that during deposition, the provenance became more mafic and less intermediate. The chemostratigraphic correlation is more detailed than is available from other stratigraphic techniques.